1. Field of the Invention
This invention relates to a system and method for curing of thermosettable materials and melting of thermoplastics in general and, more specifically, for curing die attach to leadframes for semiconductor devices.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices, an important step is that of bonding of the semiconductor die to a lead frame or the like prior to the wire bonding operations. Many processes have been used in the prior art to perform this function as discussed in S. M. Sze, VLSI Technology, 2nd Edition, pp 586-589, 1988 as well as processes developed subsequent to that publication. The predominant and most common die attach cure process used in the industry at present is a through batch cure process in a nitrogen purge convection oven. This process involves a long cure cycle time due to the slow response time of the heat source. Volatiles due to outgassing and the like may remain in the oven during processing.
With the advent of the snap cure die attach materials, other solutions that were developed were the use of heater blocks and optical lamps known as rapid cure process (RCP). In the case of both of these solutions, energy is transferred directly to the leadframe and curing of units is accomplished on a per strip basis (one leadframe strip at a time per station). The heater block makes use of conduction for heat transfer while RCP uses radiation as its primary heat transfer mechanism to cure the die attach material.
The conventional RCP cure process utilizes direct transfer of energy from lamp to target so leadframes are individually cured. This limitation hinders this procedure from supporting in-line cure of high productivity manufacturing equipment. While RCP is quite rapid in temperature response of the target, it is slow because it operates on a "line of sight" basis and cures only one leadframe at a time. It is therefore readily apparent that the prior art procedures for die attach have demonstrated a relatively low throughput.